The present invention relates to a dielectric leaky-wave antenna. More particularly, in a dielectric leaky-wave antenna for leaking an electromagnetic wave formed by a ground plane and a dielectric from a transmission guide, the present invention relates to a dielectric leaky-wave antenna having a single-layer structure which adopts a technique for enabling radiation of various kinds of polarized electromagnetic waves by a simple structure.
In recent years, demands for a planar antenna which can be used in a millimeter wave region for an automotive radar or a wireless LAN have been increasing.
As such an antenna for a millimeter wave region, there have been proposed various kinds of antenna, e.g., one for leaking an electromagnetic wave from slots provided to a wave guide, a so-called triplate antenna for feeding power through a triplate line by providing a coupling slot on a board and others.
However, among these antennas, an antenna using a wave guide is disadvantageously difficult to be manufactured since it has a three-dimensional structure partitioned by a metal wall.
Further, the triplate antenna has a large line loss although it is not as large as that of a micro-strip line, and unnecessary waves caused due to reflections of radiating elements are transmitted in the triplate line, which prevents the efficiency of the antenna to increase.
Therefore, there is proposed a parallel-plate slot array antenna in which a transmission guide which is equivalent to a wave guide is constituted by upper and lower metal surfaces of a printed board and through-holes formed so as to pieces the metal surfaces (TECHNICAL REPORT OF IEICE. A.P 99-114, RCS99-11 (199-10)).
However, the parallel-plate slot array antenna constituting the transmission guide equivalent to the wave guide by using the through-holes to the printed board as mentioned above is structurally complicated as compared with the dielectric leaky-wave antenna, and its manufacturing cost involved by processing of the through-holes is increased.
Further, in the case of this antenna, since a uniform electromagnetic field mode, i.e., a TEM mode is used in a cross section which is vertical to the transmission direction, the same strong electric current flows to the upper and lower metal plates, and the conductor loss is generated, which is a factor of occurrence of the large loss.
Furthermore, since a dielectric plate is actually inserted to the parallel plates in order to shorten the guide wavelength and suppress the grating lobe, the dielectric loss is also generated, and there is a limit in reducing the loss.
Moreover, as another type of antenna, there is proposed a leaky-wave antenna in which a dielectric rod for radiation which has a narrow width is arranged on a dielectric slab having a double-layer structure to provide a transmission line, the height of the transmission line is partially changed and metal strips are cyclically provided to lower parts (U.S. Pat. No. 4,835,543, xe2x80x9cDielectric slab antennaxe2x80x9d).
This is a one-dimensional array antenna. In order to obtain a two-dimensional antenna which is practically important, however, since a plurality of dielectric rods for radiation must be arranged, the mass production property is poor, and a power feeding system to these rods in phase becomes complicated.
Besides, there is proposed a method by which a dielectric slab having a projection portion in a direction vertical to the plate is manufactured, the surface of the slab is metalized in order to form a continuous transverse slub and the obtained slub is utilized for an antenna (U.S. Pat. No. 5,266,961 xe2x80x9cContinuous transverse slub element devices and method of making samexe2x80x9d).
This is a slot array antenna which is uniform in the transverse direction and uses a parallel-plate wave guide in which a dielectric is inserted. However, a dielectric material such as alumina is generally difficult to be processed at a high frequency of, e.g., a millimeter wave and with low loss. Manufacturing the complicated dielectric slab having many protrusions leads to the problems in cost.
Thus, there has been expected realization of a planar antenna which has a simple structure and the high efficiency and can emit various kinds of polarized electromagnetic waves respectively suitable for an automotive radar or a wireless LAN.
Therefore, the present international patent applicant (inventor) filed a patent application xe2x80x9cdielectric leaky-wave antenna (double-layer structure)xe2x80x9d to Japan (JPA2000-54487, JPA2000-22471), United States (dielectric leaky-wave antenna filed on Dec. 19, 2000) and Europe (EPA00127989. 2).
This xe2x80x9cdielectric leaky-wave antenna (double-layer structure)xe2x80x9d greatly reduces the electric currents flowing to a ground plane and the conductor loss and realizes the high efficiency by providing a small air layer between the ground plane and a dielectric slab (plate) and obtaining the double-layer structure.
Moreover, by providing such a double-layer structure, since a metal strip can be also printed on a back surface of the dielectric slab, reflection in the line can be suppressed.
In an antenna for the 76 GHz band manufactured by way of trial based on these techniques, the antenna efficiency of 76% which is far greater than the conventional antenna efficiency of approximately 50% is realized.
Meanwhile, when trying to apply the xe2x80x9cdielectric leaky-wave antenna (double-layer structure)xe2x80x9d to a low-frequency domain of a quasi-millimeter wave or a millimeter wave for wireless access (for example, FWA: Fixed Wireless Access) and the like in the 20 GHz band, the wavelength becomes approximately two fold to three fold. Therefore, the necessary thickness of the dielectric slab becomes as thick as approximately 2 mm, whereas the conventional thickness is approximately 0.6 to 0.8 mm.
Thus, such a thickness (approximately 2 mm) can not be realized easily by using alumina which is generally used for such a dielectric slab because of technical problems in manufacture. In addition, since the board having a special thickness which can not be observed in the standard size is necessary, the cost for materials is disadvantageously increased.
Therefore, the inventor of this international patent application has obtained the following knowledge by eagerly adding examination in order to apply the above-described xe2x80x9cdielectric leaky-wave antenna (double-layer structure)xe2x80x9d to communication in a quasi-millimeter wave region such as a 20 GHz band, e.g., wireless access, an indoor wireless LAN and the like, or a low-frequency domain of a millimeter wave.
At first, the important knowledge is that, by providing a xe2x80x9cdielectric leaky-wave antenna having a single-layer structurexe2x80x9d of a so-called image guide type in which a dielectric slab is laid on a ground plane, the thickness of the dielectric slab can be xc2xd of the thickness in case of applying the above-described xe2x80x9cdielectric leaky-wave antenna (double-layer structure)xe2x80x9d to the quasi-millimeter wave region (not more than approximately 1 mm). Therefore, the board having the thickness of approximately 0.6 to 0.8 mm in the standard size can be used.
Another knowledge is that, by providing such a xe2x80x9cdielectric leaky-wave antenna having a single-layer structurexe2x80x9d, although the entire conductor loss is increased as compared with the case when providing an air layer as in the above-mentioned xe2x80x9cdielectric leaky-wave antenna (double-layer structure)xe2x80x9d, the conductor loss itself is in proportion to a square-root of a frequency. Therefore, the influence of the conductor loss is relatively small in the quasi-millimeter wave region.
Still another knowledge is that, in such a xe2x80x9cdielectric leaky-wave antenna having a single-layer structurexe2x80x9d, the antenna structure in which uniform metal strip rows are provided in the transverse direction on the dielectric slab surface or a reflection suppression strip is provided on the same surface is also common to the above-described xe2x80x9cdielectric leaky-wave antenna (double-layer structure)xe2x80x9d.
In view of the above-described prior art problems and the knowledge for those problems, it is an object of the present invention to provide a dielectric leaky-wave antenna having a single-layer structure which is effective for realizing a low-cost antenna with high efficiency in a quasi-millimeter wave region in particular.
To achieve this object, according to the present invention,
(1) there is provided a dielectric leaky-wave antenna comprising:
a ground plane;
a dielectric slab which is laid on one surface of the ground plane, and forms a transmission guide for transmitting an electromagnetic wave from one end side to the other end side along the surface between the ground plane and itself;
perturbations which are loaded along the electromagnetic transmission direction of the transmission guide on the surface of the dielectric slab at predetermined intervals, and leak electromagnetic wave from the surface of the dielectric slab; and
a feed which supplies the electromagnetic wave to one end side of the transmission guide.
Further, according to the present invention,
(2) there is provided the dielectric leaky-wave antenna defined in the above (1), wherein the perturbation has a length which is substantially equal to a width of the dielectric slab, and is constituted by a metallic strip or a slot which is orthogonal to the electromagnetic wave transmission direction of the transmission guide.
Furthermore, according to the present invention,
(3) there is provided the dielectric leaky-wave antenna defined in the above (1), wherein the perturbation is constituted by a metallic strip or a slot having an angle of 45 degrees with respect to the electromagnetic wave transmission direction of the transmission guide.
Moreover, according to the present invention,
(4) there is provided the dielectric leaky-wave antenna defined in the above (2) or (3), wherein a pair of perturbations arranged in parallel to each other in such a manner that an interval along the electromagnetic wave transmission direction of the transmission guide becomes approximately xc2xc of a wavelength of the electromagnetic wave in the transmission guide are loaded at the predetermined intervals along the electromagnetic wave transmission direction of the transmission guide.
In addition, in order to achieve the-above described object, according to the present invention,
(5) there is provided a dielectric leaky-wave antenna, wherein the perturbation is constituted by a pair of metallic strips or a pair of slots which form an angle of 90 degrees and respectively have an angle of 45 degrees with respect to the electromagnetic wave transmission direction of the transmission guide.
Additionally, in order to achieve the above-described object, according to the present invention,
(6) there is provided the dielectric leaky-wave antenna defined in (5), wherein an interval between the metallic strips forming a pair or the slots forming a pair is set to approximately xc2xc or xc2xd of a wavelength of the electromagnetic wave in the transmission guide.
Further, in order to achieve the above-described object, according to the present invention,
(7) there is provided the dielectric leaky-wave antenna defined in the above (1), wherein the feed is constituted so as to radiate a cylindrical wave, and a wave-front conversion section for converting a cylindrical wave radiated from the feed into a plane wave and leading it to the transmission guide is provided to one end side of the dielectric slab.
Furthermore, in order to achieve the above-described object, according to the present invention,
(8) there is provided the dielectric leaky-wave antenna defined in the above (7), wherein the wave-front conversion section is formed by extending the dielectric slab to the feed side.
Moreover, in order to achieve the above-described object, according to the present invention,
(9) there is provided the dielectric leaky-wave antenna defined in the above (8), wherein the feed is formed so as to transmit the electromagnetic wave inputted from one end side thereof to one end side of the dielectric slab along the ground plane and radiate it from an aperture portion on the other end side formed so as to surround an edge portion on one end side of the dielectric slab, and a matching section which projects toward the ground plane side so that a gap between itself and the surface of the wave-front conversion section becomes gradually or continuously small toward the wave-front conversion section is provided to the aperture portion on the other end side of the feed in order to match the feed with the wave-front conversion section.
In addition, in order to achieve the above-described object, according to the present invention,
(10) there is provided the dielectric leaky-wave antenna defined in the above (8), wherein a matching section for matching the feed and the wave-front conversion portion and leading the electromagnetic wave supplied from the feed to the wave-front conversion section is provided to a leading end of the wave-front conversion section.
Additionally, in order to achieve the above-described object, according to the present invention,
(11) there is provided the dielectric leaky-wave antenna defined in the above (7), wherein the wave-front conversion section has a reflecting wall which converts a cylindrical wave into a plane wave and one half portion of the reflecting wall is arranged so as to face one end side of the dielectric slab, and the feed is arranged on the opposite side to the dielectric slab with the ground plane therebetween so as to illuminate the other half portion of the reflecting wall of the wave-front conversion section.
Further, in order to achieve the above-described object, according to the present invention,
(12) there is provided the dielectric leaky-wave antenna defined in the above (11), wherein a matching section for matching the wave-front conversion section with the transmission guide of the dielectric slab is provided at one end side of the dielectric slab.
Furthermore, in order to achieve the above-described object, according to the present invention,
(13) there is provided the dielectric leaky-wave antenna defined in the above (10) or (12), wherein the matching section is formed into a tapered shape so that the thickness is reduced toward the input side for the electromagnetic wave.
Moreover, in order to achieve the above-mentioned object, according to the present invention,
(14) there is provided the dielectric leaky-wave antenna defined in the above (10) or (12), wherein the matching section is constituted by a dielectric having a dielectric constant different from that of the dielectric slab.
In addition, according to the present invention, in order to achieve the above-described object,
(15) there is provided the dielectric leaky wave antenna defined in the above (12), wherein the wave-front conversion section is formed so as to transmit the electromagnetic wave reflected from the reflecting wall to one end side of the dielectric slab along the ground plane and radiate the electromagnetic wave from an aperture portion formed so as to surround an edge portion on one end side of the dielectric slab, and a matching section which protrudes to the ground plane side so that a gap between itself and the surface of the dielectric slab becomes gradually or continuously small toward the dielectric slab side is provided to the aperture portion of the wave-front conversion portion in order to match the wave-front conversion section with the transmission guide of the dielectric slab.
Additionally, according to the present invention, in order to achieve the above-described object,
(16) there is provided the dielectric leaky-wave antenna defined in the above (7), wherein the feed has a plurality of radiators having radiation center positions different from each other, and
wherein the wave-front conversion section converts a cylindrical wave radiated from each of the radiators into a plane wave whose wave front inclines at an angle corresponding to the radiation center position of that radiator and supplies the obtained wave to the transmission guide.